Preheat the oven to 325 degrees. Spray an 8 x 8 baking dish with cooking spray and set aside.
In a large bowl combine the flour, sugar, baking powder, and salt. Mix well.
In a medium bowl combine the egg, milk, vegetable oil, and vanilla. Mix well.
Pour the wet ingredients into the dry ingredients and mix until combined. Pour into the prepared pan.
In a small bowl combine the flour, brown sugar, cinnamon, salt, and butter. Mix with a fork and then sprinkle over the top of the cake.
Bake for 35-40 minutes. Remove from oven and cool completely. Cut into 9 squares.